Ultra-hard compacts are used as small cutting or wear elements in various shapes, often disks, consisting of a stiff substrate with a (preferably) high modulus of elasticity such as cemented carbide. This preferably stiff substrate supports an ultra-hard cutting layer typically containing diamond or CBN (cubic boron nitride) and possibly other materials such as sintering aids, binders, and secondary abrasives. The ultra-hard layer is used as the cutting or wear resistant cutting surface, and is typically found on the cutting faces of rock drills and other industrial cutting tools required to cut or drill through hard, abrasive materials.
While the above description of an ultra-hard compact is representative of commercially available compacts, the composition of the substrate/ultra hard layer compact can vary in a manner known to those skilled in the art. For example, a substrate may comprise something other than carbide-type materials when used in applications that do not demand high loading conditions. The ultra-hard layer may comprise multiple layers of different composition, or a layer which varies from one side to the other, and may be flat or curved or irregular. There may be non-planar interfaces between differing materials on the compact interior. In addition, there may be chip breakers or special contours on the exterior surfaces. These and other known variations will be apparent to those skilled in the art.
The commercially available geometry and extreme hardness of ultra-hard compacts renders them difficult to attach and replace on cutting tools such as rock drills. Prior art methods of attachment typically involve brazing the substrate onto the tool face, but there are several problems inherent in the brazing method of attachment. The part onto which the PCD is being brazed needs to be heated with special equipment; brazing skill, like welding skill, is variable among operators; certain tools and environments do not tolerate the heat involved in the brazing process; brazing can cause thermal damage to the PCD compact itself; and, brazed ultra-hard compacts are difficult to replace or repair.
There have been attempts to improve the manner in which hard cutting elements are attached to cutting tools. For example, U.S. Pat. No. 4,694,918 to Hall discloses a PCD compact having a cylindrical portion sized for a press-fit into a drill bit or similar tool surface. The compacts are embedded in the bit by press-fitting or brazing them into the head of the bit.
U.S. Pat. No. 4,057,884 to Suzuki discloses a tool holder in which a cemented carbide type cutting bit has a hole formed through it for attachment to a tool with a bolt mechanism. The Suzuki attachment structure is designed for a compact with uniform (non-ultra hard) material having an angular, lateral cutting edge, rather than a PCD type compact with an ultra-hard cutting face.
U.S. Pat. Nos. 3,136,615 and 3,141,746 mention without explanation the use of "mechanical joints" to secure a cutting compact to a tool, for example: "mechanical joints also may be employed in the compact oriented in holder 27 in various arrangements depending on compact configuration" (column 4, lines 64-66 of the '746 patent). Also: "The compact is attached to some support in various position by soldering or brazing, for example, a titanium hydride soldering process as given in U.S. Pat. No. 2,570,428, Kelley, or by mechanical attaching means, or by having the tool or adjacent metal be forced into the surface irregularities of the compact" (column 6, lines 17-23 of the '746 patent).
U.S. Pat. No. 4,199,035 to Thompson discloses a threaded attachment system for mounting a stud- or pin-shaped PCD compact on a drill bit by way of an external threaded sleeve mating with a threaded bushing in the drill bit. The sleeve holds the compact in place in an interference-type fit as it is threaded down into the tool-mounted bushing over the compact. This patent additionally discloses a metal locating pin mounted on the tool to slide fit into a recess in the lower surface of the stud toward the edge of the stud to locate the stud at the proper rotational angle for cutting.
The above-described prior art has not fully satisfied the need for a simple, efficient method for attaching PCD compacts to a tool or other support surface. The invention described below solves this problem.